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Special Issues. Contact Us. Colloid and Surface Science. The current research work centred on the micellization of binary system of Cetylpyridinium chloride CpyCl and cetyltrimethylammonium bromide CTABr in the absence and presence of nonionic hydrotropes i. The critical micelle concentrations CMC , at different mixed mole fraction of mixed surfactant were evaluated.
Activity coefficient, ideal CMC, micellar mole fraction, interaction and thermodynamic parameters were obtained using theoretical Clint and Rubingh models. The interaction parameter values were all negative, signifying strong interaction between the mixed surfactant. The evaluated thermodynamic parameters were all negative, indicating spontaneity and stability of the mixed micelle formed.
Mandeep SB, Singh J, Kulbir S, Kaur G Mixed micelles of cationic gemini with tetraalkyl ammonium and phosphonium surfactants: the head group and hydrophobic tail contributions.enter
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Colloids and Surfaces A: Physicochem. Langmnir ; Study of micellization of sodium dodecyl sulfate in non-aqueous media containing lauric acid and dimethylsulfoxide. Surfactants Deterg ; Interaction of cetrimide with nonionic surfactant-Triton X and Brijj A Conductrimetric and Tensiometric study. Surfact Deterg ; Langmuir ; Rosen MJ. Synergism in mixtures containing zwitterionic surfactants. Would you like to change to the United States site?
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Added to Your Shopping Cart. Materials and methods. The cationic surfactant CTAB was purified by recrystallization three times from dry ethanol to obtain the pure surfactant ascertained using elemental and 1 H NMR data , Scheme 1. Surface tension measurements.
Conductivity measurements. The electrode was washed after each reading several times with deionised water. Micellar mole fraction X 1 , X ideal. In aqueous medium, the surfactant solutions of low concentration behave as simple electrolyte solutions and most of the surfactant molecules exist as free monomers. However, above a certain concentration, known as critical micelle concentration cmc , micelles start to form. In a homogeneous series, the cmc of surfactants is related to the number of carbon atoms in the hydrophobic chain. The surfactant chain length is a major driving factor for micellization 33 and hydrophobic interactions a major driving force.
Entropy increases when water molecules in hydration shell around the hydrophobic parts of monomeric amphiphiles are released during micelle formation. As the length of hydrophobic chain increases, more water molecules are released resulting in more entropy increase, hence micellization occurs at lower concentration, i. Addition of one methylene group -CH 2 in the hydrophobic chain halves the cmc value. However, effect of head group and counter ion on cmc is comparatively lesser.
It is reported that replacement of methyl group of dodecyl trimethyl ammonium bromide by an ethyl group decreases the cmc from Figure 1 represents the variation of surface tension vs. It is clear that increasing the hydrophobic chain length of the dimethyl alkyl phosphine oxide surfactants considerably decreases their cmc values. Comparing the obtained data of the pure components surface tension at equilibrium, surface excess and critical micelle concentration values with the published data 33 showed good agreement with some deviation which can be attributed to the need of further purification for the components used.
Figure 2 represents the variation of surface tension vs. The cmc values of the different solutions were extracted from Figure 2 and listed in Table 1.
The ideality of the mixing process can be evaluated to determine the ideal value of the critical micelle concentration cmc ideal at certain bulk mole fractions using Clint equation based on the pseudophase thermodynamic model 17 as follows:. This equation makes difference between ideal and nonideal surfactant mixtures. All the figures show that the cmc values of each mixture vary nonlinearly with respect to the regular change in bulk mole fraction. Due to the presence of cationic head groups in combination with those of bulky nonionic phosphine oxide head groups in the stern layer of the mixed micelle, a nonideal behaviour is expected in the mixed state.
It is clear from data represented in Table 1 that the experimental cmc values cmc exp of different mole fraction combinations of CTAB-dimethylalkyl phosphineoxide, determined from the surface tension-log C plots, are always lower than the theoretical cmc values of each individual component and also from the ideal values cmc ideal. The lower cmc exp values compared to cmc ideal is attributed to the attractive interactions between the two mixed components. This attraction moves the surfactant chains from monomeric phase to micellar phase, which facilitates the formation of the mixed micelles and decreases the free energy of the system.
The ideal contribution of component i in the formed mixed micellar system composed of different components can be calculated in term of mixed mole fraction in the ideal state X ideal as follows: 4. A quantitative interpretation of the results can be carried out by considering the regular solution theory RST and the treatment proposed by Rubingh. The values of X 1 were obtained by solving Equation 3 iteratively.
Values of X ideal and X i were recorded in Table 1 and plotted in Figure 4 for the different mixed systems. While in the rich regions of CTAB 0. A higher X 1 than that of corresponding X ideal value indicates that the mixed micelles have high contribution of the cationic component than the nonionic component, while a lower X 1 than X ideal value suggests the poor cationic content in the mixed micelles. That suggests the nonideality of the mixed systems at the lower mole fractions. Decreasing the difference between X 1 and X ideal indicates the increase of ideality extent in the behaviour of the mixed system.
Ideal system has not any type of interaction between the different components, and also low free energy. That was explained from the regular solution theory point of view. In the regular solution theory, the molecules in the mixed system are assumed to be of comparable volume, completely interchangeable. In case of X 1 higher than X ideal , the system shows nonideal behaviour synergism. The synergistic effect occurs due to the difference in hydrophobicity of the mixed surfactant. The micellization occurs at lower cmc than cmc 1 and cmc 2 ; thus due to the richness of CTAB in the bulk of the solution, a high participation of CTAB molecules in the formed mixed micelles occurs.
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Due to the hydrophobicity factor and the incompatibility between the decyl and hexadecyl hydrophobic chains and the repulsion between head groups. Increasing the difference between the hydrophobic chain length of the cationic and nonionic components, i. That is called the hydrophobic effect. The partially high negative charged head group is due to the high inductive effect of the tetradecyl and hexadecyl chains. The more hydrophobic component is preferentially adsorbed at the interface and consequently pumps the less hydrophobic components to the bulk.